Compositions – Electrolytes for electrical devices
Reexamination Certificate
2000-09-12
2002-10-15
Koslow, C. Melissa (Department: 1755)
Compositions
Electrolytes for electrical devices
C252S062550, C264S212000, C264S216000, C264S429000, C264S427000
Reexamination Certificate
active
06464894
ABSTRACT:
FIELD OF THE INVENTION
The invention concerns a hard magnetic film with a polymer base particularly intended for use in electric motors or sensor applications and a method for the production thereof.
BACKGROUND OF THE INVENTION
Owing to the continued trend to miniaturization in the field of electronics there is an increasing demand for particularly small or flat electric motors. These motors, which conventionally contain hard magnetic components in the stator and/or rotor, naturally require particularly flat magnetic components. Similarly there is an increasing demand for particularly flat permanent magnets for miniature relays and sensors functioning on magnetic principles (such as rotation or position sensors). In addition these magnets should be as flexible as possible so that if desired they may be brought to the desired shape after magnetization and may avoid breakage during processing or in operation.
According to conventional methods utilized for the production of permanent magnets from powdered metallic or non-metallic magnetic materials, the cost-effective production of flat objects with a low thickness of for example 100 &mgr;m and high energy density is impossible.
SUMMARY OF THE INVENTION
The task of the present invention therefore was to make available a flexible hard magnetic material with low thickness and a cost-effective method for the production thereof.
It was found that the application of casting technology enables the production of carrier-free hard magnetic films from a polymer matrix and a hard magnetic powder distributed therein. The term “carrier-free” signifies that the finished films—unlike for example those films already known from magnetic tapes or floppy disks—are constructed not from a non-magnetic carrier and a single- or double-sided layer capable of magnetization, but from a single continuous layer that is magnetic or capable of magnetization. The hard magnetic powder has usefully a median particle size of less than 100 &mgr;m, preferably less than 20 &mgr;m.
Films according to the invention advantageously have a thickness of 50 to 2000 &mgr;m, preferably one of 100 to 500 &mgr;m.
The volume fraction of the hard magnetic powder in magnetic film according to the invention can be adjusted as desired. The preferred value is at least 50% but especially preferred is at least 60%. The polymer fraction can be kept so low that the polymer effectively occupies simply the voids in an approximately dense packing of the powder particles.
In films according to the invention the preferred content of hard magnetic powder consists of one or more rare earth alloy(s). Within the scope of the invention, however, other hard magnetic materials can be employed, for instance Al-Ni-Co or Cr-Fe-Co alloys or ferrites.
Particularly preferred are rare earth alloys described by the general formulas RECo
5
, (RE)
2
(Co,Fe,Cu,Zr)
17
or (RE)
2
Fe
14
B. Here RE signifies an element from the group consisting of yttrium, lanthanum, cerium, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium and lutetium or a mixture of several of these elements. Most particularly preferred are the compounds Sm
2
(Co,Fe,Cu,Zr)
17
and (Pr,Nd,Dy)Fe
14
B. Alloys of these types are available for example under the brand names VACOMAX® and VACODYM® from the company Vacuumschmelze GmbH or the brand name MAGNEQUENCH® from the company Magnequench Inc. References herein to “(Co,Fe,Cu,Zr)” refer to the listed elements generally in the disjunctive (in other words, “one or more of Co or Fe or Cu or Zr”). Likewise, the preceding use of “(Pr,Nd,Dy”) refers to the listed elements in this manner.
The polymer matrix can basically consist of any polymer that is soluble or dispersible in volatile solvent. It is also possible to utilize polymers that are available in appropriate forms of thin layers of low-viscosity monomers or oligomers. In these instances the use of solvent during production can be omitted where desired. It is preferable to utilize soluble thermoplastic material, particularly soluble polyvinylidene fluoride. It is, however, also possible to utilize non-thermoplastic material such as single-component polyurethane dispersions.
The hard magnetic powder particles can be aligned in no particular order (isotropic) or, if they display inherent anisotropy, can be aligned as desired. They are preferably aligned parallel or vertical to the surface of the film.
The residual magnetism of magnetic films according to the invention is determined by the type and packing density of hard magnetic powder particles and has a preferred value of 0.2 to 0.8 tesla.
Magnetic films according to the invention can for example by produced by (i) dispersing a powder of hard magnetic material in a solution or dispersion of polymer material in a volatile solvent, (ii) casting the dispersion thus obtained as a film of defined thickness on a revolving casting belt, (iii) evaporating the solvent and (iv) withdrawing the film thus formed from the casting belt. The film can be magnetized after evaporation of the solvent or at a later time (for example after fabrication), such that the binding of the magnetic particles in the polymer matrix yields an isotropic magnetic film.
In a preferred form of the method according to the invention the orientation of the hard magnetic powder particles is created by means of an external magnetic field between the casting process and withdrawal of the film.
Particularly preferred is an orientation before hardening of the cast film. Particles of an anisotropic material can here by aligned in an external magnetic field so as to yield an anisotropic magnetic film.
Magnetization and alignment where desired can be carried out preferably by means of pulsed magnetic field. Here the use of electromagnetic can enable high field strengths with low energy consumption. Hard magnetic powder particles for which orientation is particularly easy can also be orientated in the air gap of an appropriate permanent magnet yoke.
A preferred material for the hard magnetic powder is a rare earth alloy.
Particularly preferred are rare earth alloys described by the general formulas RECo
5
, (RE)
2
(Co,Fe,Cu,Zr)
17
or (RE)
2
Fe
14
B where RE signifies one or more of the elements Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb or Lu.
A preferred material for the polymer is soluble polyvinylidene fluoride (copolymer).
A preferred volatile solvent for soluble polyvinylidene fluoride (copolymer) is acetone.
The revolving casting belt consists preferably of dull special steel.
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patent: 3070841 (1963-01-01), Schornsteimer
patent: 3467598 (1969-09-01), Kroenke
patent: 3764539 (1973-10-01), Cochardt et al.
patent: 4200457 (1980-04-01), Beck
patent: 4562019 (1985-12-01), Inoue
patent: 4881988 (1989-11-01), Bonser
patent: 5607768 (1997-03-01), Lee
patent: 5888417 (1999-03-01), Akioka et al.
patent: 2456121 (1975-07-01), None
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patent: 0274034 (1988-07-01), None
patent: 274034 (1988-07-01), None
patent: 1-313903 (1989-12-01), None
Derwent abstract for JP 1-313903, attached to JP 1-313903.*
Abstract of Japanese Patent Document No. 01313903 (Dec. 19, 1989).
Antochin Sergej
Fernengel Wilhelm
Katter Matthias
Rodewald Werner
Wall Boris
Kilpatrick & Stockton LLP
Koslow C. Melissa
Russell Dean W.
Vacuumschmelze GmbH
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